Utils tool class problems

 

When performing a performance test, I found a problem with an MD5 tool class. under heavy pressure, I encountered a computing error. I analyzed the code and found the cause.

Here is the original code:

 

Public class MD5 {

 

// -------------------------------------------------------------- Private data

Private static SecureRandom random = null;

Private static MessageDigest md = null;

 

// -------------------------------------------------------------- Constructors

 

/** Creates a new instance of MD5 */

Protected MD5 (){

}

 

// ------------------------------------------------------------ Public methods

 

/**

* Returns a new nonce to be used for MD5 authentication. The nonce bytes

* Are guaranteed to be in the printable range from ascii 32 to 128.

*

* @ Return a new 16 bytes long nonce

*/

Public static byte [] getNextNonce (){

Byte [] nextNonce = new byte [16];

Random. nextBytes (nextNonce );

 

Int I;

For (int j = 0; j <nextNonce. length; ++ j ){

I = nextNonce [j] & 0x000000ff;

If (I <32) | (I> 128 )){

NextNonce [j] = (byte) (32 + (I % 64 ));

}

}

 

Return nextNonce;

}

 

/**

* MD5ies the given content

*

* @ Param data the data to be digested

*

*/

Public static byte [] digest (byte [] data ){

Md. reset ();

Return md. digest (data );

}

 

// ----------------------------------------------------------- Private methods

 

/**

* Creates and initialize the random generator. Called ad class loading

* Time.

*/

Private static void randomGeneratorInit ()

Throws java. security. NoSuchAlgorithmException {

Random = SecureRandom. getInstance ("SHA1PRNG ");

}

 

// --------------------------------------------------------------- Static code

 

Static {

Try {

RandomGeneratorInit ();

Md = MessageDigest. getInstance ("MD5 ");

} Catch (Exception e ){

E. printStackTrace ();

}

}

}

 

Here is the modified Code:

 

Public class MD5 {

 

// -------------------------------------------------------------- Private data

Private static SecureRandom random = null;

Private static MessageDigest md = null;

 

// -------------------------------------------------------------- Constructors

 

/** Creates a new instance of MD5 */

Protected MD5 (){

}

 

// ------------------------------------------------------------ Public methods

 

/**

* Returns a new nonce to be used for MD5 authentication. The nonce bytes

* Are guaranteed to be in the printable range from ascii 32 to 128.

*

* @ Return a new 16 bytes long nonce

*/

Public static byte [] getNextNonce (){

Byte [] nextNonce = new byte [16];

Random. nextBytes (nextNonce );

 

Int I;

For (int j = 0; j <nextNonce. length; ++ j ){

I = nextNonce [j] & 0x000000ff;

If (I <32) | (I> 128 )){

NextNonce [j] = (byte) (32 + (I % 64 ));

}

}

 

Return nextNonce;

}

 

/**

* MD5ies the given content

*

* @ Param data the data to be digested

*

*/

Public static byte [] digest (byte [] data ){

Synchronized (md ){

Md. reset ();

Return md. digest (data );

}

 

}

 

// ----------------------------------------------------------- Private methods

 

/**

* Creates and initialize the random generator. Called ad class loading

* Time.

*/

Private static void randomGeneratorInit ()

Throws java. security. NoSuchAlgorithmException {

Random = SecureRandom. getInstance ("SHA1PRNG ");

}

 

// --------------------------------------------------------------- Static code

 

Static {

Try {

RandomGeneratorInit ();

Md = MessageDigest. getInstance ("MD5 ");

} Catch (Exception e ){

E. printStackTrace ();

}

}

}

The main differences are as follows:

Synchronized (md ){

Md. reset ();

Return md. digest (data );

}

 

 

 

This article is from the "Hai Li Bu's column" blog